This invention relates to computed tomography and more particularly to a cable-handling system for use in a computed tomography machine.
Medical diagnoses are frequently made with the help of cross-sectional patient images developed through a procedure formerly known as computerized axial tomography (CAT) and now generally referred to as simply computed tomography (CT). With all current CT machines, an X-ray tube is moved in an orbital path about a patient.
With so-called translate-rotate (TR) machines, an X-ray tube and a paired detector array are moved linearly as the X-ray tube is energized and data is collected. After the lineal or translational movement along a given path has been completed, the source/detector pair are orbited incrementally typically for about 20.degree. of rotation. After the incremental orbiting has been completed, the source and detector are scanned linearly once again and further data is collected. This alternate lineal translation and orbital motion is repeated until the desired data has been collected for production of a so-called reconstructed image.
Other machines are in use in which the X-ray tube and a connected array of detectors are orbited about an axis which intercepts the patient. Data is collected during the orbital movement.
More recently, stationary detector (SD) machines have been developed. With SD machines a fixed annular array of detectors is provided. An X-ray tube is orbited about an axis which is also the axis of the detector array. The tube is orbited at a high rate of speed so that the data collection to produce an image is completed in as little as one second.
The provision of electrical power to the X-ray tube and associated elements of a tube head assembly is essential to the operation of any of these machines. Usually the X-ray tube is of the type that employs a rotating anode and a thermionic filament. It is necessary to provide filament current to heat the filament, power to the motor which rotates the anode and the high-tension current used to direct an electron beam from the cathode to the anode. Often the tube will also be equipped with a focusing cup and/or a grid which also requires power. In addition, other components of the tube head assembly may require power. Examples are motors to drive collimator elements, a filter drive motor and a light to indicate collimator position.
In most if not all current CT machines, power is supplied to the X-ray tube head assembly through flexible conduits or cables. Since the X-ray tube is orbited about the patient, the problem of playing out and retrieving these electrical cables is considerable. The problem is magnified in that the cable must be kept free of a patient positioning aperture through the center of the machine. The problem is further complicated by the high speed, repetitive movement of the cables through an extremely high number of cycles. As a consequence, cable breakage due to so-called cable fatigue, i.e. cold working of the conductive metal, has troubled CT manufacturers and users.
There have been many proposals for dealing with so-called cable take-up in CT machines. While there have been many such proposals, non has been fully satisfactory and none has uniformly distributed the cable flexing over the entire slack portion of the cable with a controlled bend having a relatively large radius of curvature so as to minimize the cable fatigue.